The invention relates to a monocular telescope. More specifically, the invention relates to a monocular telescope having a constant length and a focusing unit whose mechanical sensitivity depends on the chosen magnification.
German Offenlegungsschrift 20 05 396, published Jan. 7, 1971, discloses a telescope with a focusing device in which a rotatable focusing drive mechanism acts on a focusing element which is axially displaceable in the tube of the telescope. A cam with a hermetically sealed sliding surface is provided as a geared connection between the focusing drive mechanism and the focusing element. The entire focusing range is covered by a half to a whole revolution of the focusing drive mechanism, with the direction of rotation of the focusing drive mechanism remaining the same. In order to step up or reduce the magnitude of the displacement achieved by the cam, a transmission gear is provided between the cam and the focusing element. This telescope has a constant magnification and a fixed eyepiece.
German Auslegeschrift 11 09 398, published Jun. 22, 1961, discloses a telescope with variable magnification whose eyepiece tube is extended to different lengths depending on the chosen magnification. The eyepiece tube is guided in a cam sleeve. A cam slot is provided for positive rotation when changing the extension. The cam slot is coupled in a longitudinally displaceable but relatively non-rotatable fashion to a carrier of an erecting structure which is guided by a second cam slot for positive displacement during rotation of the cam sleeve. As a result, large changes in the telescope magnification can be achieved. Focusing is performed by means of a fine adjustment nut. The focus adjustment, once set for a specific distance, is retained over the entire magnification range.
U.S. Pat. No. 3,028,792, issued Apr. 10, 1962, discloses a telescope with continuously variable magnification which has two coaxial rotating knobs which are arranged in a housing recess and are separated by a divider. The rotating knob on the lens side displaces a focusing lens via a threaded shaft for the purpose of focusing. The rotating knob on the eyepiece side is used to change the magnification by means of two axially displaceable lenses whose movement is controlled by a spiral cam.
A monocular telescope having a constant length is also known. In such a telescope, it is possible to achieve a stepwise variation in the magnification, for example, 20-, 30-, and 40-fold, by means of an interchangeable eyepiece. It is also possible to achieve a continuously variable magnification setting, for example, 20- to 60-fold, using a zoom eyepiece. Focusing is performed manually by means of a control knob whose rotary movement effects the axial displacement of a focusing element. Due to a shallow depth of focus at high magnifications, it is difficult to focus the telescope using the control knob because the focal plane is traversed too quickly. Analogous problems occur at low magnifications, i.e., it takes too long to adjust the focus. For these reasons the rate of focus adjustment is designed for an average magnification value.